Substance use disorders (SUD) in persons with severe mental illness (SMI) are common and have a profound effect on the course of psychiatric illness. Despite the prominence of "dual disorders" among the SMI, no manualized, empirically validated treatments exist. There is a particular need for family work in this area because most dually diagnosed clients maintain contact with relatives, and the loss of family support is associated with housing instability and homelessness in this population. The proposed research will be a controlled evaluation of a new family intervention for dual disorders (FIDD) program, described in a treatment manual and supported by a pilot study. The study will take place at two typical public mental health centers, the North Suffolk Mental Health Association in Massachusetts and the San Fernando Mental Health Center in California. The research will be conducted by the joint effort of two well-established centers for mental health services and clinical trials research, the New Hampshire-Dartmouth Psychiatric Research Center and the UCLA Intervention Research Center. A total of 140 clients and their families (N=70 at each site) will be randomly assigned to either the FIDD program for 2 years (N=70), which includes both single family and multiple-family group formats, or family psychoeducation including 6 weekly sessions (N=70). Fidelity of clinicians to the FIDD program will be monitored with standardized measures. Routine assessments will be conducted over 2 years on all clients and relatives to evaluate a wide range of outcomes, including substance abuse, hospitalizations, psychiatric symptoms, legal problems, aggression, housing and homelessness, family burden, social support, and quality of life. Process measures of the FIDD program will include family knowledge of dual disorders and problem-solving skill. The results of the proposed research have important implications for improving the long-term outcomes of clients with dual disorders and lessening the impact of SUD on relatives. Enhancing the skills of families for coping with dual disorders is expected to be an effective strategy for treating SUD, decreasing hospitalizations, and decreasing caregiver burden. Improvements in these areas may the have long-term benefit of maintaining family involvement with dually diagnosed clients, thereby reducing housing instability and homelessness.